Morphometric Analysis of Axis and Its Clinical Significance -An Anatomical Study of Indian Human Axis Vertebrae.

Abstract

The atlas and axis vertebra have unique shape and complex relationship with vertebral artery. Fracture of dens of axis accounts for 7-27% of all cervical spine fractures, but surgeries in these regions are highly risky because of the reported incidences of vertebral artery injury. The study was designed to measure morphometric data of human axis vertebra, of Indian origin. The different anatomical parameters on dry specimen of human axis vertebrae were established and the results were compared with other studies. Thirty intact human axis vertebrae were measured with digital vernier caliper and mini-inclinometer. Various linear and angular parameters of axis were observed. The mean distance from the midline of body to the tip of transverse process of axis was 29.32 mm on right side and 29.06mm on left side. The mean distance from the midline of body to the lateral most edge of superior articulating facet was 22.8 mm on right side and 22.6 mm on left side. The mean value of anterior and posterior height of axis was 34.33±2.69mm and 30.56±2.78mm respectively. The anterior and posterior height of body of axis was 19.67 mm and 16.67mm respectively. Mean A-P and transverse diameter of inferior surface of axis was 15.42mm and 17.7mm respectively. Mean transverse diameter and mean A-P diameter of odontoid process was 9.32 mm and 10.1 mm respectively. Mean anterior and posterior height of the odontoid process was 14.66 mm and 13.89mm respectively. Mean of dens axis sagittal angle (angle between an axis that was imagined to pass longitudinally through the dens axis and the vertical line on a sagittal plane) was 13.23 degree. The shape of superior articulating facets of C2 varies from oval to circular. In the present study, 84% of SAF were oval and 16% were circular. Inferior articulating facets were circular in shape in 90% cases, and oval in 10% vertebra. Mean pedicle width was 10.07mm on right side and 10.52mm on left side. Mean transverse diameter of vertebral canal was 22.37±1.73mm. Mean of A-P diameter of vertebral canal at inlet was 18.31±2.05mm and mean of A-P diameter of vertebral canal at outlet was 14.84±1.63mm. These results obtained from this study may be helpful for the surgeons in avoiding and minimizing complications such as vertebral artery injury, cranial nerve damage and injury to other vital structures while doing surgery around cranio-vertebral region.